The present invention relates relates to current production by homopolar generators, and more particularly to pulsatile, high current generation by the conversion of inertial energy stored in the rotor of a homopolar generator to electric current, and the discharge of the electric current from the generator to an external circuit or workpiece.
Homopolar generators have been successfully designed for providing pulsed discharges lasting a few seconds and producing a peak current level in excess of a million amperes direct current. Such generators generally include a cylindrical rotor of either a drum or disc configuration, mounted on a frame, to be rotated about an axis through the center of the cylinder. A field coil encircling the rotor and connected to an external current supply provides an applied field excitation passing through the rotor. The applied field excitation is usually confined and directed by a ferromagnetic yoke surrounding the field coil and all, or a portion of, the rotor. When the rotor is spinning, the free electrons within the rotor experience an electromotive force resulting from their interaction with the applied field excitation. Brushes, positioned inside the field coil or between two halves of the field coil, are then lowered onto the spinning rotor to allow a current to flow under the influence of such electromotive force through return conductors to an external circuit, and then back into the rotor through additional brushes at a different location. During the discharge, the interaction of the discharge current and the applied field excitation creates a force which decelerates the rotor until its rotation stops and the discharge therefore ends. It has been found, as mentioned above, that extremely high current pulses may be obtained after using a relatively low power conventional prime mover or a conventional low voltage, low amperage power source to store inertial energy in the rotor by gradually motoring the rotor up to the desired rotational speed.
The general state of the art relating to pulse power homopolar generators is shown in the following publications which are incorporated herein by reference: H. H. Woodson, H. G. Rylander, W. F. Weldon, M. D. Driga, E. B. Becker, K. M. Tolk, R. C. Swanson, C. Ramage, J. M. Weldon, M. Hart, "Homopolar Motor-Generator for Inexpensive Inertial Energy Storage," Texas Atomic Energy Research Foundation Report, Progress Report No. 22, Nov. 1, 1974; W. F. Weldon, M. D. Driga, H. H. Woodson, H. G. Rylander, "The Design, Fabrication, and Testing of a Five Megajoule Homopolar Motor-Generator," International Conference on Energy Storage, Compression, and Switching, Torino, Italy, Nov. 5-7, 1974 (Reprint, University of Texas Departments of Mechanical and Electrical Engineering); R. C. Swanson, Editor, "Progress Report No. 1, Homopolar Motor-Generator Research for Inertial Energy Storage," University of Texas, Energy Storage Group report to the Energy Research and Development Administration, June, 1975.
In order to effectively conduct a current from or to the spinning rotor, the stationary brushes of the homopolar must be made of a relatively soft conductive material such as graphite or copper-graphite. The brushes are biased against the rotor surface during discharge, and are subject to constant wear. Therefore the brushes must be periodically replaced, and access to the brushes is necessary. Access may also be required for maintenance of the brush retractor mechanism and electrical connections to the brushes.
In order to avoid dismantling the massive yoke to reach the brushes, prior art homopolar generators have included ports through the rotor or removable ferromagnetic plugs extending through the rotor. Service lines such as compressed air lines for operating the brush retractor mechanism have passed through the ports or have been carried by the plugs. Such openings have passed either axially through the yoke below the field coil, or radially through the yoke if the field coil was split into two halves on either side of the brushes. Such openings not fitted with ferromatnetic plugs have been made as small as possible to minimize disruption of the magnetic field confined and directed by the yoke. Thus, access to the brushes and associated apparatus has been obtained only by reaching far into the generator structure with an arm or tool that tended to obstruct vision of the work being performed, and to make such work awkward and difficult. Furthermore, if the field coil is split to allow such access the two halves of the field coil exert a significant force on one another, so that the apparatus must be built with greater structural strength.
Similar brush access has been provided in electric motor generators such as that disclosed in U.S. Pat. No. 1,805,935, issued to Weathers.